* Scenes of bruised, beaten athletes raise health alarm
* Science suggests brain mechanism kicks in to prevent harm
* Experts say no-one can die from intensity of exercise
By Kate Kelland
LONDON, Aug 9 (Reuters) - When a rower is helped from his boat after a race robs him of the ability to walk, and a triathlete is put on an intravenous drip after winning bronze then collapsing, people wonder if being an Olympic athlete is good for your health.
The London 2012 Games have seen bleeding, broken and bruised athletes get back up and push themselves harder, faster and further in pursuit of gold.
It is a time of extremes, but scientific evidence suggests no-one will push beyond the limit.
"You'll never die because of intensity of exercise," said Gregoire Millet, director of the Sport Science Institute at the University of Lausanne in Switzerland. "You will never die because you push yourself so hard."
Experts point to a body of scientific work that explores the issues of exercising to exhaustion, or fatigue, among top-class athletes. What it suggests is reassuring for anyone who is worried these athletes are killing themselves.
Research, much of it led by Tim Noakes, a professor of exercise and sports science at the University of Cape Town in South Africa, suggests that however much some athletes may want to push beyond all previous performances, a switch in the brain - known as the "central governor" - will keep them safe.
"The brain uses the symptoms of fatigue as key regulators to ensure that the exercise is completed before harm develops," Noakes wrote in a recent paper in the journal Frontiers In Physiology.
In other words, it's not that muscles get too exhausted to work any more, or that the body gets too hot to go on, but that the brain stops an athlete activating the same amount of muscle, thus forcing them to stop before it's "life over".
For Richard Budgett, chief medical officer at the London 2012 Games and the man charged above all else with protecting athletes' health, having the "central governor" around is a good thing.
Himself a former Olympic gold-medal winning rower - he won in a coxed four alongside Steve Redgrave at the 1984 Los Angeles Games - Budgett says seeing people compete until they collapse, buckle or vomit, doesn't make him feel uncomfortable.
"In fact it fills me with enormous respect," he told Reuters in an interview. "This is all about exploring human limits.
"Rowers in training, for example, they fall off rowing machines and vomit and all the rest of it - but an hour later they're back doing more training.
"And we have that central governor that stops us from actually killing ourselves. People can't carry on through the point of doing themselves real damage."
Budgett is also eager to point out that many myths about potentially negative health effects of many years of hard exercise are generally not borne out by the scientific evidence.
Studies in weightlifters, for example - who many might suspect would suffer lower back pain and damage as they get older - show that these athletes actually have less back pain in later life than other people.
A scientific paper published in 1997 on the health status of former elite athletes from Finland found those who focused on aerobic sports in particular had long, healthy life expectancy and low risk of heart disease and diabetes in later years.
While these athletes had a slightly higher than normal risk of developing osteoarthritis - a condition marathon runner Paula Radcliffe has struggled with in recent years - the research concluded the benefits of a physically active lifestyle on health were "clearly higher" than any adverse effects.
"Of course if you sit on a couch all day, you're not going to get hurt," said Budgett. "And undoubtedly when people are pushing themselves right to the limit, some of them will get injuries or collapse.
"But that's the way we are made. As humans we do like to do this. We see people going to the north pole, and climbing Everest. It's not just at the Olympics.
"It's really interesting to see how hard people can push themselves when they're at this kind of once-in-a-lifetime event." (Editing by Mike Collett-White)